Characteristics can be improved by providing a layer in which Fe is introduce at a position under a channel layer in a high electron mobility transistor (HEMT) which contains a gallium nitride (GaN)-based material. Fe forms a deep acceptor level in the vicinity of valence band of GaN, and an electron is captured in the acceptor level, so that leakage current in a thickness direction is suppressed, and pinch-off characteristics are improved.
However, Fe may be diffused from the layer doped with Fe to a region in which two-dimensional electron gas (2DEG) exists in the channel layer, and in this case, mobility of electron is lowered. A structure is proposed for the purpose of suppressing the reduction in the mobility of electron as above, in which a layer of AlN or AlGaN whose Al composition exceeds 40% is disposed between the layer doped with Fe and the GaN channel layer. However, even with this structure, it is not possible to obtain sufficient characteristics.
Patent Literature 1: Japanese Laid-Open Patent Publication No. 2010-182872
Patent Literature 2: Japanese Laid-Open Patent Publication No. 2010-232297
Patent Literature 3: Japanese Laid-Open Patent Publication No. 2008-288474
Patent Literature 4: Japanese Laid-Open Patent Publication No. 2008-251966